As an alternative to standard whip antennas and roof mount mast antennas, automotive vehicle window antennas have been used for many years including embedded wire or silver print antennas in rear windows and windshields. More recently, metal coated infrared ray reflective thin films have been used as antennas for vehicles. Other antenna arrangements incorporate a slot antenna between the metal frame of a vehicle window and a conductive transparent film panel that is bonded to the window and has an outer peripheral edge spaced from the inner edge of the window frame to define the slot antenna. Various such arrangements utilize at least one edge of the conductive coating overlapping the window frame of the vehicle body to form a short to the ground at high frequencies by coupling to improve transmission and reception of radio frequency waves.
With rapid growth in the performance requirements of vehicle electronics, more and more antennas have been integrated into vehicles. At FM and TV frequencies in particular, antenna systems require a number of antennas for diversity operation to overcome multipath and fading effects. In existing systems, separate antennas and antenna feeds are used to meet such requirements. For example, up to 11 antennas with separate feed points and multiple modules have been used to cover AM, FM/TV diversity, weather band, Remote Keyless Entry, and DAB Band III, with most of the antennas being integrated into back window glass. Multiple coaxial cables running from antennas to the receiver can be avoided by combining the separate antenna signals using an electrical network. Such a network, however, involves the added complexity and expense of a separate module. Thus, in order to limit the complexity and expense of an on-glass antenna system, it may be desirable to keep the number of antenna feeds to a minimum.
Thus, there is a need for a single feed antenna, in particular an IR reflective windshield antenna, that provides wide bandwidth characteristics for different applications. There is also a need for an antenna system that reduces the number of antennas on a vehicle and simplifies the antenna and its associated electronics by using antenna matching and frequency tuning methods. It is desirable for such an antenna to meet system performance requirements while retaining the solar benefits of the heat reflective coating of the window while maintaining good aesthetics.